Pedigree analysis of pre-breeding efforts in Trifolium spp. germplasm in New Zealand

Background Prebreeding in plants is the activity designed to identify useful characteristics from wild germplasm and its integration in breeding programs. Prebreeding aims to introduce new variation into the populations of a species of interest. Pedigree analysis is a valuable tool for evaluation of variation in genebanks where pedigree maps are used to visualize and describe population structure and variation within these populations. Margot Forde Germplasm Centre (MFGC) is New Zealand’s national forage genebank and holds a collection of ~ 75 species of the genus Trifolium, of which only a dozen have been taken through prebreeding programs. The main objective of this study was to construct pedigree maps and analyse patterns of relatedness for seven minor Trifolium species accessions contained at the MFGC. These species are Trifolium ambiguum, Trifolium arvense, Trifolium dubium, Trifolium hybridum, Trifolium medium, Trifolium subterraneum and the Trifolium repens x Trifolium occidentale interspecific hybrids. We present a history of Trifolium spp. prebreeding in New Zealand and inform breeders of possible alternative forage species to use. Results Pedigree data from accessions introduced between 1950 and 2016 were used and filtered based on breeding activity. Kinship levels among Trifolium spp. remained below 8% and no inbreeding was found. Influential ancestors that contributed largely to populations structure were identified. The Australian cultivar ‘Monaro’ had a strong influence over the whole population of accessions in T. ambiguum. T. subterraneum and T. repens x T. occidentale had the largest number of generations (3). T. ambiguum and T. medium had the highest cumulative kinship across the decades. Conclusions We conclude that there are high levels of diversity in the seven Trifolium spp. studied. However, collection and prebreeding efforts must be strengthened to maximize utilization and bring useful genetic variation.

Diversity pattern of nitrogen fixing microbes in nodules of <i>Trifolium arvense</i> (L.) at different initial stages of ecosystem development

Legumes can be considered as pioneer plants during ecosystem development, as they form a symbiosis with different nitrogen fixing rhizobia species, which enable the plants to grow on soils with low available nitrogen content. In this study we compared the abundance and diversity of nitrogen fixing microbes based on the functional marker gene nifH, which codes for a subunit of the Fe-protein of the dinitrogenase reductase, in nodules of different size classes of Trifolium arvense (L.). Additionally, carbon and nitrogen contents of the bulk soil and plant material were measured. Plants were harvested from different sites, reflecting 2 (2a) and 5 (5a) yr of ecosystem development, of an opencast lignite mining area in the south of Cottbus, Lower Lusatia (Germany) where the artificial catchment "Chicken Creek" was constructed to study the development of terrestrial ecosystems. Plants from the 5a site revealed higher amounts of carbon and nitrogen, although nifH gene abundances in the nodules and carbon and nitrogen contents between the two soils did not differ significantly. Analysis of the nifH clone libraries showed a significant effect of the nodule size on the community composition of nitrogen fixing microbes. Medium sized nodules (2–5 mm) contained a uniform community composed of Rhizobium leguminosarum bv. trifolii, whereas the small nodules (<2 mm) consisted of a diverse community including clones with non-Rhizobium nifH gene sequences. Regarding the impact of the soil age on the community composition a clear distinction between the small and the medium nodules can be made. While clone libraries from the medium nodules were pretty similar at both soil ages, soil age had a significant effect on the community compositions of the small nodules, where the proportion of R. leguminosarum bv. trifolii increased with soil age.

Diversity pattern of nitrogen fixing microbes in nodules of <i>Trifolium arvense</i> (L.) at different initial stages of ecosystem development

Legumes can be considered as pioneer plants during ecosystem development, as they form a symbiosis with different nitrogen fixing rhizobia species, which enable the plants to grow on soils with low available nitrogen content. In this study we compared the abundance and diversity of nitrogen fixing microbes based on the functional marker gene nifH, which codes for a subunit of the Fe-protein of the dinitrogenase reductase, in nodules of different size classes of Trifolium arvense (L.). Additionally, carbon and nitrogen contents of the bulk soil and plant material were measured. Plants were harvested from different sites, reflecting 2 (2a) and 5 (5a) yr of ecosystem development, of an opencast lignite mining area in the south of Cottbus, Lower Lusatia (Germany) where the artificial catchment "Chicken Creek" was constructed to study the development of terrestrial ecosystems. Plants from the 5a site revealed higher amounts of carbon and nitrogen, although nifH gene abundances in the nodules and carbon and nitrogen contents between the two soils did not differ significantly. Analysis of the nifH clone libraries showed a significant effect of the nodule size on the community composition of nitrogen fixing microbes. Medium sized nodules (2–5 mm) contained a uniform community composed of Rhizobium leguminosarum bv. trifolii, whereas the small nodules (< 2 mm) consisted of a diverse community including clones with non-Rhizobium nifH gene sequences. Regarding the impact of the soil age on the community composition a clear distinction between the small and the medium nodules can be made. While clone libraries from the medium nodules were pretty similar at both soil ages, soil age had a significant effect on the community compositions of the small nodules, where the proportion of R. leguminosarum bv. trifolii increased with soil age.

Root system variability in common legumes in Central Europe

The aim of this study was to provide an overview of field measured root systems of common legume species growing under different environmental conditions in the Czech Republic. The plants, 214 individuals of 21 selected legume species from the tribes Galegeae (Astragalus glycyphyllos, Lupinus polyphyllus), Genisteae (Cytisus scoparius, Genista tinctoria), Loteae (Anthyllis vulneraria, Lotus corniculatus, Securigera varia), Trifolieae (Trifolium arvense, T. campestre, T. medium, T. pratense, T. repens) and Vicieae (Lathyrus pratensis, L. sylvestris, Vicia angustifolia, V. cracca, V. hirsuta), were collected using the monolith method from 27 sites.A rhizome was present in seven species and the maximum branching order was three for 15 species and five for five species. Recovery buds were recorded on the root system of eight species and woodiness was recorded in 11 species. Root diameter ranged from 1 to 12 mm — the minimum diameter was recorded in annuals and the maximum in perennials. The colour of the root system ranged from light to dark. In six species, young roots were light and older roots were dark. Globose, cylindrical, branched, fan-like and ruff-like nodules were recorded. Only one type of nodule shape was recorded in 11 species, two in seven species and three or four in three species. Nodules measured up to 2 mm in nine species, from 2 to 4 mm in three species and more than 4 mm in nine species. Legume root systems are highly variable and the variability was due to Raunkier’s life forms rather than membership of a tribe.

The ecology of four annual clovers adventive in New Zealand grasslands

Four annual clovers have become adapted to the dry and semi-arid grasslands in New Zealand. In the absence of competition from perennial clovers, which are adapted to sub-humid and humid environments, further spread is likely to continue. Annuals rely on high numbers of small and hard seeds for survival. Their germination is dependent on a combination of adequate soil moisture and favourable temperatures, with no evidence of a prechilling treatment required. For striated clover, germination results highlight their adaptation to cool moist autumn conditions during germination. The benefits of adventive clovers for N fixation (0.2-100 kg N ha-1) are greatest where sulphur fertiliser has been applied, the clover population is dense, and soil moisture ideal over several months, but may be nil in drought conditions. Key words: annual clovers, germination, nitrogen fixation, semi-arid grassland, Trifolium arvense, T. dubium, T. glomeratum, T. striatum